We are only about 24 hours past this shooting. NPR's Tom Gjelten, you've been covering this all day. And I want to ask you, what do you think we should expect that of the investigation tomorrow and in the coming days?

TOM GJELTEN, BYLINE: The big question obviously, Robert, is, why in the world would this relatively wealthy white guy with a comfortable life, 64 years old, living in a golfing community, apparently come up with this mission to kill as many people as he possibly can? It just baffles the mind. We'll be looking for answers to that very mysterious question. We'll be looking for answers in the electronic devices. I assume that means iPads or laptops that they have found in his home. They'll be wanting to talk to his girlfriend who is...

SIEGEL: She's said to be out of the country.

GJELTEN: She's out of the country. She's apparently in Tokyo. And presumably, you know, they lived together. She must have known something about what was going on. So they do have avenues to pursue here in order to answer that question.

SIEGEL: You say she must know something because if, in fact, the guns that he had at home that were found today and the guns that he took to the hotel - if they were in his possession before all of this - he had an arsenal at his house.

GJELTEN: He had more than 18 weapons at his house. It's hard to hide those from the person you're living with.

SIEGEL: Also we would expect to learn something about how he came by automatic weapons or at least an automatic weapon.

GJELTEN: I think the ATF, the Alcohol Tobacco and Firearm Department, would be very anxious to find out who, if anyone, provided those weapons to him.

SIEGEL: And presumably after all of the security footage from the Mandalay Bay Resort is examined, we might have some sense of how exactly and when he brought all of these weapons to his hotel room.

GJELTEN: Yeah. I'm sure that these security people will want to know that. We'll also want to know what happened in the - you know, the final timeline. I mean, did he in fact shoot himself? Was he shot by people coming to his room? There's still some questions about that final timeline.

SIEGEL: There's a hole in the timeline.

GJELTEN: Well, yes, because no one says that the shooting lasted longer than 15 minutes. And yet it was an hour before that SWAT team finally breached his room. So there's like a 45 minute gap there. Was he dead all that time, or was he there but just not shooting anymore? We don't know that.

SIEGEL: Questions that will be - we hope to be hearing answers to in the coming days. Transcript provided by NPR, Copyright NPR.